Couplings for power cables typically comprise coupling elements which are locked by means of a bayonet connector. Since both coupling elements, i.e. the plug part and the socket part, are solidly made according to the state of the art, a rigid connection is attained which remains in the locked position only due to the friction forces.
In order to maintain a largest possible friction force, a normal force is produced via a bayonet mechanism, said normal force pressing the plug and the socket together. Moreover, a strong normal force is important for maintaining a low-impedance electric transition between the plug part and the socket part.
Consequently, couplings having a plug part, a bayonet mechanism, and a socket part are generally used in welding installations. In fact, the DIN EN 60974-12 standard “Coupling devices for welding cables” exists as a standard for conventional connectors used in welding technology, and many components found in the market are configured in accordance with this standard. The components differ from producer to producer due to numerous remaining liberties in design and construction when it comes to the standard's application. Consequently, an ideal compatibility is not readily ensured.
A problem which commonly occurs in practice is that the plug connections known thus far can detach of their own accord after a period of time. This may be because of purely constructive principles, as both the plug part and the socket part are comparatively rigid components. After locking the plug connection, only a very slight elastic deformation of the parts is possible so that the contact surfaces are immediately lifted upon the slightest back rotation of the connectors and the normal force between the components drops to zero. In this condition, the electric contact resistance of the contact increases dramatically.
In practice, the described detachment process often arises due to mechanical vibrations, an increase in the temperature of the plug connectors during operation and heat expansions connected thereto and/or contact surfaces behaviors. Consequently, an even larger and irregular increase in the temperature of the components occurs via the increased contact resistance, which can amplify the effect.
The increase in temperature can further lead to damage to the connectors, their insulation, the connected cables, and/or machine parts.
In welding installations, increased contact resistance in a connection, which often fluctuates in dependence of vibrations, often causes a temporally variable drop in voltage in the power-cable connection and thus in the electric circuit when there is a loose connection. Through this, the electric arc voltage is involuntarily influenced; the quality of the welding process can drop or become instable.